Evaluation of the absorbed dose of the thyroid gland in conventional spiral and spiral computed tomography techniques

Introduction: The use of sophisticated radiographic techniques is absolutely necessary in dentistry. The use of these techniques exposes the sensitive organs of head and neck to x-rays. The aim of the present study was to investigate the absorbed dose of the thyroid gland in conventional spiral and spiral computed tomography techniques. Materials and Methods: In this experimental study, 10 TLD GR-200 circular dosimeters (Thermoluminans Detector) were used in male RANDO-like phantom (head and neck segment, i.e. the first 10 segments) in order to determine the radiation dose absorbed by the thyroid gland. Then spiral computed tomographies were provided from the anterior and posterior regions of the maxilla and mandible along with a lateral Scout view as a guide. Conventional spiral tomographies were prepared from the maxilla, mandible and both jaws with a panoramic radiograph as a guide. Data was analyzed using Kruskal-Wallis and Mann-Whitney tests using SPSS 11.5 (a = 0.05). Results: The highest and lowest thyroid gland absorbed doses were observed with computed tomography of both jaws and conventional spiral tomography of the anterior maxilla, respectively (5.92 ± 0.01 and 0.79 ± 0.01 mSiv). The mean amount of the absorbed dose by the thyroid gland was lower in the conventional spiral tomography compared to computed tomography. The two techniques revealed significant differences in the absorbed doses except for conventional spiral tomography in the posterior and anterior regions of the mandible (p value = 0.276).Conclusion: According to results of the present study, the absorbed dose of the thyroid gland in the conventional spiral tomography in different regions of the jaws was less than CT scan techniques. As a result, it appears the use of conventional spiral tomography is preferred over CT scans in limited regions where three-dimensional and cross-sectional views are required.Key words: Thyroid gland, Film dosimetry, Spiral Computed Tomography.